(1) Field of the Invention
This invention relates to the deposition of metallic coatings from plating solutions as well as anodizing of metals. More particularly, this invention relates to wiping the cathodic coating surface of sheet and strip during continuous electroplating as well as the anodic sheet or web during continuous anodizing and also to electrolytic cleaning of metallic workpieces and more particularly still to the use of a substantially solid wiper blade and open web, plastic mesh separators during such electroplating, anodizing or electrolytic cleaning.
(2) Prior Art
As detailed more particularly in U.S. application Ser. No. 08/316,530 filed Sep. 30, 1994, the disclosure of which is hereby expressly incorporated in and made a part of the present application, a number of coatings are deposited from so-called plating baths subjected to an imposed electrical potential basically enhancing an already naturally occurring tendency for metal ions in the solution to plate out.
Since the coating of a cathodic workpiece is largely merely the acceleration of a naturally occurring process or phenomena, fairly small changes in technique and apparatus accentuating those conditions that favor deposition and de-emphasizing these conditions that disfavor deposition, may have rather large effects upon the final coating obtained. The history of improvements in the field, therefore, is largely one of progressive small improvements and adjustments to improve the conditions for deposition of various coating metals on a metallic substrate temporarily included as the cathode in a plating circuit.
It has been found, for example, by the present inventors as well as others that it is conducive to good coating results to remove the hydrogen bubbles which are produced at the cathodic work surface by transfer of electrons not only to the positive ions of the coating metal in the solution, but also to positive hydrogen ions in the electrolytic solution. The initial cathodic film is believed to be a combination or mixture of both hydrogen ions and atomic or molecular hydrogen. This film initially is only one atom thick. It interferes to some extent with good coating in that it may tend to hold the larger metallic coating ions away from the surface to be coated. However, the hydrogen atoms are small and the layer of hydrogen is initially discontinuous so that their initial interference with coating is not too serious.
If nothing is done to remove the hydrogen from the surface coating during the coating process, coating will usually continue, even though it may be seriously interfered with by the increasing hydrogen present as the thickness of the hydrogen layer increases the interference with efficient plating out of metal atoms upon the substrate surface. Such hydrogen, as it accumulates, however, tends to coalesce into larger local accumulations resulting in small bubbles and then larger and larger bubbles until such bubbles have sufficient volume and buoyancy to overcome their initial attraction for or adhesion to the substrate surface and float upwardly in the solution to the surface where they are finally dissipated into the surrounding atmosphere or local environment. Consequently, the hindrance to coating caused by the presence of hydrogen gas at the surface of a cathodic workpiece does not tend to progress to the limit where it would cut off electrolytic plating completely. However, hydrogen is still a very significant hindrance to rapid coating or plating and the larger bubbles clinging to the surface of a workpiece may even lead to macroscopic pits and other defects in an electrolytic coating.
A second significant problem which has been long recognized in electrolytic coating baths is depletion of the electrolytic solution as coating progresses. In many cases, the only result is that the coating rate slows down as there are progressively less coating metal ions in the solution to plate out. This decreasing coating rate has been counteracted by pumping in fresh coating solution, throwing in chunks of soluble coating metal for solution to "beef up" the electrolyte as well as other expedients. The trend has been for closer and closer control of the electrolyte composition during coating. Sometimes this has been implemented by continuous testing or analysis of the electrolytic bath as coating progresses. In addition, the coating solution baths have been mixed by impellers or the like, force circulated and re-circulated as well as frequently tested to hold them to a desired composition.
It has also been recognized that the coating bath next to a workpiece being coated may become locally depleted of coating metal ions and that such depletion may compromise efficient coating. Some installations have adopted the expedient of forced circulation of electrolyte past the point of coating or through a restricted coating area to increase the efficiency of coating. If the forced circulation is rapid enough, such circulation in itself also tends to detach bubbles of hydrogen from the cathodic coating surface, in effect, "killing two birds with one stone". However, the use of forced circulation of this type by pumps, jets and the like is not only unwieldy and expensive, but is believed by some to possibly have detrimental effects upon the coating itself because of the generalized rapidity of movement between the coating solution and cathodic workpiece, which macroscopically, at least, may interfere with efficient plating out of the metallic ions upon such work surface. Among the processes which have made use of rapid forced circulation is the so-called gap coating process in which a small coating gap between a coating anode and a cathodic workpiece is created and electrolytic solution is forced rapidly through such gap or opening.
Depletion of the coating solution has recently been found by one of the present inventors to be particularly serious in chrome plating solutions in which insoluble electrodes are used. It has been found that unless the chromium plating operation is maintained substantially continuous and at a fairly uniform rate that hard chrome is difficult to efficiently plate out in a brush-type coating operation, or, for that matter, in semi-brush type operations.
While various efforts to remove hydrogen bubbles from the coating surface in an electrolytic coating bath at the point of deposition have been tried, none has provided the ultimate quality of coating and efficiency of the coating operation which has been desired. Likewise, the ultimate in practical prevention of localized depletion in a coating bath has also not been attained.
A further problem in the continuous coating of a flexible material such as sheet, strip and wire products is that the efficiency of electroplating usually increases as the spacing between the electrodes, one of which is the material to be coated, decreases. In other words, the efficiency of coating is usually inversely related to the spacing between the electrodes one of which is the workpiece. However, due to the flexibility of the material being coated, it must, as a practical matter, be held away from the opposing electrode a sufficient distance to prevent arcing between the cathodic work material and the coating electrodes or anodes. The longer the unsupported run of material past the coating electrodes, the more deviation of the flexible material from its intended path is likely to occur, while closer spacing of supporting rolls or the like decreases the area available for coating and interferes with continuous coating. Very close spacing of the coating electrodes and the material being coated has been effected by the so-called jet coating process alluded to previously, but such process is complicated and sensitive to minor changes, making it suitable only for highly sophisticated coating lines.
There has been a need, therefore, for a means for removing hydrogen bubbles and cathodic film from a cathodic coating surface, preventing localized depletion of the coating bath with respect to coating material as well as allowing closer spacing of the coating electrodes and material being coated. The present applicants have found that a very effective means for accomplishing all three of these purposes is by the use of a relatively thin wiping blade applied to the surface of the workpiece at spaced intervals with a light contact. Such wiping blade deviates or strips away from the coating surface the relatively stable surface layer of electrolyte which tends to be drawn along with a moving cathodic surface, mixing and encouraging replenishing of the electrolyte next to the cathodic surface. It also at the same time wipes or sweeps away bubbles of hydrogen as well as encourages coalescence of small bubbles and films of hydrogen into large bubbles for subsequent wiping away. In addition, the wiping blade very effectively supports the material being coated, particularly in the case of relatively flexible material, and prevents its deviation from its intended path and, therefore, allows closer spacing of the coating electrodes and the surface of the material being coated.
The present inventors have also found that some of the same benefits attained in electro-coating are likewise obtained in the process of anodizing if the discontinuous blades of the invention are used to prevent the accumulation of bubbles of oxygen on the anodic workpiece and also to decrease the heating of the solution next to the anodic workpiece while permitting closer spacing between the anodic workpiece and the cathodic electrodes. The flexible wiping blades of the invention also significantly reduce the power requirements of the process, other things being equal, by allowing closer approach of the workpiece and the adjacent electrodes.
The present inventors have also now found that their preferred flexible wiping blades can often be replaced by contact of the surface of the strip with a plastic mesh arrangement and preferably a transversely flexible plastic mesh which serves to space the strip from adjacent electrodes as well as particularly interrupt passage of any barrier layer on the surface of the strip.
Some of the more pertinent prior art patents generally illustrating the history of the development of various solutions to some of the above-noted problems, particularly with respect to electrocoating, are as follows:
U.S. Pat. No. 442,428 issued Dec. 9, 1890 to F. E. Elmore.
U.S. Pat. No. 817,419 issued Apr. 10, 1906 to O. Dieffenbach.
U.S. Pat. No. 850,912 issued Apr. 23, 1907 to T. A. Edison.
U.S. Pat. No. 1,051,556 issued Jan. 28, 1913 to S. Consigliere.
U.S. Pat. No. 1,236,438 issued Aug. 14, 1917 to N. Huggins.
U.S. Pat. No. 1,473,060 issued Nov. 6, 1923 to E. N. Taylor.
U.S. Pat. No. 1,494,152, issued May 13, 1924 to S. O. Cowper-Coles.
U.S. Pat. No. 2,473,290 issued Jun. 14, 1949 to G. E. Millard.
U.S. Pat. No. 3,183,176 issued May 11, 1965 to B. A. Schwartz, Jr.
U.S. Pat. No. 3,619,383 issued Nov. 5, 1971 to S. Eisner.
U.S. Pat. No. 3,715,299 issued Feb. 6, 1973 to R. Anderson et al.
U.S. Pat. No. 3,751,346 issued Aug. 7, 1973 to M. P. Ellis et al.
U.S. Pat. No. 3,772,164 issued Nov. 13, 1973 to M. P. Ellis et al.
U.S. Pat. No. 3,886,053 issued May 27, 1975 to J. M. Leland.
U.S. Pat. No. 4,039,398 issued Aug. 2, 1977 to K. Furuya.
U.S. Pat. No. 4,125,447 issued Nov. 14, 1978 to K. R. Bachert.
U.S. Pat. No. 4,176,015 issued Nov. 27, 1979 to S. Angelini.
U.S. Pat. No. 4,210,497 issued Jul. 1, 1980 to K. R. Loqvist et al.
U.S. Pat. No. 4,235,691 issued Nov. 25, 1980 to K. R. Loqvist.
U.S. Pat. No. 4,399,019 issued Aug. 16, 1983 to W. A. Kruper et al.
U.S. Pat. No. 4,406,761 issued Sep. 15, 1983 to T. Shimogori et al.
U.S. Pat. No. 4,595,464 issued Jun. 17, 1986 to J. E. Bacon et al.
U.S. Pat. No. 4,652,346 issued Mar. 24, 1987 to N. W. Polan.
U.S. Pat. No. 4,828,653 issued May 9, 1989 to C. Traini et al.
U.S. Pat. No. 4,853,099 issued Aug. 1, 1989 to G. W. Smith.
U.S. Pat. No. 4,931,150 issued Jun. 5, 1990 to G. W. Smith.
Some prior patents related to anodizing as well as some of the above problems are as follows:
U.S. Pat. No. 3,074,857 issued Jan. 22, 1963 to D. Altenpohl.
U.S. Pat. No. 3,650,910 issued Mar. 21, 1972 to G. W. Froman.
U.S. Pat. No. 3,865,700 issued Feb. 11, 1975 to H. A. Fromson.
U.S. Pat. No. 4,152,221 issued May 1, 1979 to F. G. Schaedel.
U.S. Pat. No. 4,502,933 issued Mar. 5, 1985 to T. Mori et al.
U.S. Pat. No. 4,248,674 issued Feb. 3, 1981 to H. W. Leyh.
The following patents from the above compilation of patents are particularly illustrative of some of the more interesting disclosures of problems and solutions found in the above listed prior art.
U.S. Pat. No. 1,473,060, issued Nov. 6, 1923 to E. N. Taylor, discloses the use of a brush-type wiper in a coating tank environment to remove small gas bubbles and solid impurities from the coating surface intermittently (about 3 seconds out of every minute of coating) allowing the coating process to proceed uninterrupted during the time the brush is not operating.
U.S. Pat. No. 1,494,152, issued May 13, 1924 to S. O. Cowper-Coles, contains an early disclosure of a depleted layer of electrolyte carried around adjacent to the surface of a cathodic workpiece as well as bubbles of gas on the surface. The Cowper-Coles solution to these problems is to rapidly oscillate the cathodic workpiece to in effect shake off the bubbles and depletion layer (referred to by Cowper-Coles as the cathodic layer). The brushing takes place above the electrolyte surface as the hoop-type workpiece rotates into and out of the electrolyte.
U.S. Pat. No. 2,473,290 issued Jun. 14, 1949 to G. E. Millard discloses an electroplating apparatus for plating crankshafts and the like with chromium in which a curved anode partially surrounds the portion of the workpiece to be coated. The curved anode has orifices in its surfaces to allow the escape of bubbles formed during the coating process and also has extending through its surface, a support for a so-called positioning block or scraper block 54 which is provided to maintain a close spacing between the anode and cathodic workpiece. Millard states also that his spacing block removes gas bubbles from the cathode and also removes threads of chromium. He also states that the block, which has a significant width along the line of coating, dresses and polishes the cathode during plating. The aim of Millard, is clearly to burnish or compact the coating surface somewhat in the manner of the earlier Huggins patent. While Millard talks, therefore, about scraping off the gas bubbles and also removing "threads" of chromium by which it is understood that he means dendritic material, he is primarily interested in conducting a burnishing operation and spacing his cathode from his anode by his relatively wide spacer block.
U.S. Pat. No. 2,844,529 issued Jul. 22, 1958 to A. Cybriwsky et al. discloses a process and apparatus for rapidly anodizing aluminum. The Cybriwsky patent proposes maintaining a constant temperature differential between the aluminum surface and the electrolytic bath. Contact rolls are spaced throughout the apparatus but are not used for the purposes of removing gas bubbles from the metal strip.
U.S. Pat. No. 3,079,308 issued Feb. 26, 1963 to E. R. Ramirez et al. discloses a typical process of anodizing including a pumping means to transfer electrolyte onto the surface of the metal strip. A contact cell is used to provide a positive charge on the anode. There is no disclosure of a method for removing gas bubbles from the strip.
U.S. Pat. No. 3,183,176 issued May 11, 1965 to B. A. Schwartz, Jr., discloses the electrolytic treatment or coating of a bore by use of a brush coating apparatus mounted on a drill press. The inside of the bore is acted upon by a series of centrifugally extended rotating vanes having dielectric outer covers.
U.S. Pat. No. 3,359,189 issued Dec. 19, 1967 to W. E. Cooke et al. discloses a continuous anodizing process and apparatus wherein the turbulent longitudinal flow of electrolyte (as opposed to the more traditional streamline flow), either concurrent or countercurrent along the continuous workpiece, allows for increased thickness of anode oxide coating films. The Cooke et al. patent does not fully explain why increasing the turbulence of the electrolyte flow bolsters the coating efficiency. It is believed by Cooke et al., however, that the turbulent electrolyte helps disperse heat from the coating surface.
U.S. Pat. No. 3,619,383 issued Nov. 9, 1971 to S. Eisner which discloses an abrasive belt which "activates" the surface of the material being treated for electro-deposition. The activation of the surface of the sheet is said to improve the electroplating of such sheet. Eisner actually prefers to place an abrasive material on his dielectric belt to make sure that the surface is actually abraded and consequently "activated" by it. The preferred abrasive medium is a continuous belt formed of a compressed fibrous nonwoven abrasive member. The aim is to gouge the surfaces and in this way activate the surfaces of the metal to be electroplated. As a practical matter, the dielectric belt of Eisner would be quickly destroyed by any real continuous sheet processing operation by the burrs, wavy edges and lap welds of the base metal which have little effect upon the Applicant's relatively smooth generally planar open-web, plastic mesh separator material. The Eisner arrangement, furthermore, is a short contact arrangement, i.e. contact is at the surface of the guide roll, which increases the abrading of the workpiece surface, but has none of the advantages of Applicant's broader contact arrangement.
U.S. Pat. No. 3,650,910 issued Mar. 21, 1972 to G. W. Froman discloses a method for anodizing an aluminized steel strip wherein gas bubbles (both H2 and 02) are prevented from accumulating on the strip by moving the strip at faster speeds. The speed, as disclosed in the specification, is approximately 30 feet/minute. The Froman technique is an entirely different approach from both the use of a flexible wiper means and the electrolyte agitation technique described above to remedy the problem of bubble accumulation.
U.S. Pat. No. 3,715,299, issued Feb. 6, 1973 to R. Anderson et al. includes a disclosure of plastic vanes positioned close to a workpiece to cause turbulence and break up a boundary layer upon an adjacent cathodic workpiece. Anderson et al. does not directly sweep away the boundary layer or gas bubbles, but only causes turbulence and believes this at least partially breaks up and discourages the formation of a boundary layer.
U.S. Pat. No. 4,039,398 issued Aug. 2, 1977 to K. Furuya shows a series of chambers formed of dielectric material in which various operations on the strip being electroplated are carried out. Such operations are, for example, water-washing, plating, electrolytic degreasing, pickling and the like. In effect, dielectric fingers in each chamber serve to keep the strip passing through the apparatus from contacting electrodes in the outside portions of the structures. Flexible blades at the ends of the chambers serve to close off the ends of the dielectric chambers to keep the strip material passing through from dragging out with it an electrolytic solution which is separately circulated through each of the chambers. The same type of blades prevent electrolyte from leaking out of the chambers as the strip enters such chamber. The wiping blades of Furuya are not associated with Furuya's electrodes in any way. Furuya's blades are a frequent expedient at the ends of liquid or gas containing apparatus and in the case at least of liquid containment apparatus are generally referred to as end dams. Sometimes so called "double end dams" are used. Such structures do not participate in facilitation of the reactions in the apparatus in any way since their only function is to retain fluid within the apparatus and as such are contacted, if they work effectively, only on one surface by the fluid.
U.S. Pat. No. 4,125,447 issued Nov. 14, 1978 to K. R. Bachert, discloses the use of a brush attached to a movable anode within a hollow member being electroplated. The brush comprises a plurality of bristles made from plastic or other insulated material which rub against the inside surface of the tube being electroplated as the anode vibrates.
U.S. Pat. No. 4,176,015 issued Nov. 27, 1979 to S. Angelini, discloses the brushing of the surface of a series of bars as they are passed in a straight line through an anode immersed within an electroplating bath. The brushing is provided by a glass fiber brush comprising a blade having a layer of fiber scraping material compressed between side plates which is said to remove a cathodic film from the coated surface.
U.S. Pat. No. 4,210,497 issued Jul. 1, 1980 to K. R. Loqvist et al. discloses the coating of hollow members including movement inside the cavity of such members of an electrolytic solution by means of a "conveyor" which consists of a resiliently and electrically insulating material such as perforated, net-like or fibrous strip which is wound helically around a reciprocating anode. The function of the resilient electrically insulated material is to act as a conveyor of electrolyte, foam and gases which can be supplemented by forming the anode as a screw conveyor.
U.S. Pat. No. 4,227,291 issued Oct. 14, 1980 to J. C. Shumacher discloses an energy efficient process for the continuous production of thin semiconductor films on metallic substrates. The process is a cathodic deposition of germanium or silicon from an electrolyte upon an aluminum-coated steel substrate. The patent thus discloses a cathodic coating process rather than an anodizing process. The patent discloses, however, a suction apparatus that removes spent electrolyte and recirculates it. There is no device used for the specific purpose of removing gas from the vicinity of the strip, including no flexible wiping blades.
U.S. Pat. No. 4,235,691 issued Nov. 25, 1980 to K. R. Loqvist, discloses the use of angular plastic wiping blades upon the surface of a round workpiece during electroplating. The angular plastic blades are mounted in a cylindrical mounting that rotates about the round work piece. Bubbles of hydrogen are wiped from the surface by the blades.
U.S. Pat. No. 4,248,674 issued Feb. 3, 1981 to H. W. Lehy discloses an anodizing process for producing anodized aluminum stock for lithography in which a differential anodized coating is placed on the two sides. The operation of a contact cell is explained and the use of a perforated cathode disclosed to facilitate circulation of electrolyte. No use of thin wiper blades or the removal of gases from the strip or foil surface is disclosed.
U.S. Pat. No. 4,399,019 issued Aug. 16, 1983 to W. A. Kruper et al. discloses a modified tank type coating process and apparatus in which a boundary layer is broken up on an interior coating surface by use of a series of mixing blades or vanes. Kruper et al. uses "mixing blades or vanes," and preferably moving blades to essentially stir up his electrolytic solution between a perforated anode and the interior surface of his workpieces and, therefore, disturb or mix the boundary layer which develops on the work surface, which boundary layer becomes quickly depleted of coating material and replace it with a mixture of depleted and fresh electrolytic solution. Kruper et al. uses hard plastic vanes attached to his perforated anode. The plastic vanes are more or less triangular in shape or cross section with one side of the top attached to the perforated anode, the other side of the top forming the leading edge of the blade, and the base forming the trailing edge of the blade. As the blades move in a circle within the space between the internal surfaces of the bearing housings which are to be coated and the surface of the moving or rotating anode, the flat leading surface of the blades stirs the electrolytic solution and causes turbulence which mixes the solution in the working space and causes flow both inwardly and outwardly through the orifices in the rotating anode assembly into and from the main body of coating solution within the center of the perforated anode assembly. Kruper et al. indicates that he prefers to maintain a space between his stirring blades and the coating surface of the workpiece. However, in an incidental disclosure without details, Kruper et al. also indicates that the stirring blade could less desirably extend to the coated surface and in such case it is preferred that the blades be somewhat resilient such as in a windshield wiper or a brush. Exactly what sort of shape this would be is not clear, but it seems clear in either case that the resiliency would cause the triangular structure shown to be compressed inwardly, forming a seal between the blade and the coated surface interfering with the electrocoating operation.
U.S. Pat. No. 4,406,761 issued September 1983 to T. Shimogori et al. is directed to de-scaling metal sheets, especially titanium and stainless steel, by anodic electrolysis. To facilitate such electrolysis, the sheet surfaces are subjected to an abrading operation. The so-called "abrasive member" is slid relative to the strip during electrolysis in order to increase diffusion of metal ions from the sheet surface and thereby increase de-scaling and cleaning. It is stated that the abrasive member, which is preferably in the form of a continuous three-strand woven belt with included abrasive materials within the woven construction, may be various other materials and structures such as emery cloth, an abrasive belt, an abrasive brush or an abrasive roll. It is stated, however, that an abrasive belt and abrasive brush are particularly effective and suited for continuous treatment.
U.S. Pat. No. 4,502,933 issued Mar. 5, 1985 to T. Mori et al. discloses an apparatus for electrolytic treatment including anodizing of a metal web. The Mori et al. patent addresses the problem of gas accumulation and provides some historical background noting past solutions in this area. According to the Mori et al. patent, electrolyte agitation appears to be the traditional solution towards reducing bubble formation. Because electrolyte agitation requires a much larger pump, however, the added power consumption negates the cost-saving benefits from the removal of the gas. Another solution noted by Mori et al. has been transporting the aluminum web vertically through the bath. Problems stemming from this technique include supplying sufficient power to the metal web and the added maintenance cost of the unusual design. Finally, a partition plate method is stated by Mori et al. to be disclosed in Japanese Patent Publication No. 21840/80 wherein partition plates extend "along the length" of the aluminum web in the bath and apparently perpendicular to the aluminum web in the bath. The partition plates form a channel which intensifies the agitation of the electrolyte. By narrowing the region with the plates, the agitation removes the bubbles from the metal surface more effectively. This technique, like the first technique described, requires a larger pump and therefore suffers from the same disadvantages. The Mori et al. patent, like the other techniques, attempts to remove bubbles by agitating the flow of electrolyte. Electrical insulating members extend transverse of the direction of a metal web and above the level of the electrodes adjacent the web surface and therefore spaced from the web surface to allegedly vigorously agitate the electrolyte in the vicinity of the web.
U.S. Pat. No. 4,595,464 issued Jun. 17, 1986 to J. E. Bacon et al., discloses the use of a so-called brush belt for continuously treating a workpiece. The brush belt is in the form of a continuous loop which passes over suitable rollers or pulleys and brings plating solution in the brush portion to the plating area. Essentially, Bacon et al. provides an absorbent belt which passes in opposition to the material to be coated.
U.S. Pat. No. 4,652,346 issued Mar. 24, 1987 to N. W. Polan discloses the coating of a very thin foil. In order to prevent such foil from waving or fluctuating, Polan runs or passes it over a dielectric framework which prevents the foil from bending or oscillating out of the normal passline. In a sense, Polan does insulate the workpiece from adjacent electrodes by use of a dielectric material. However, such dielectric material is not a mesh-type material. Polan teaches that a very thin workpiece or strip can be passed through electrolytic processing operations on a frame to prevent it from bending or folding, but does not teach the use of a separator between the workpiece or strip and adjacent electrodes to establish a minimum spacing between the two, although Polan talks about the maintenance of a constant gap, i.e. his dielectric framework is not really a practical solution to the problem, however. Polan clearly thought he had to use fairly large openings and did not realize the possibility of using a unitary material having multiple orifices in it through which electrolyte solution can freely pass.
U.S. Pat. No. 4,828,653 issued May 9, 1989 to C. Traini et al. discloses a so-called dimensionally stable anode for high-speed galvanizing processes. Such anode has a composite construction disclosed in several embodiments. The first such embodiment is fairly typical. The electrode is comprised of several conductive layers referred to as foraminous layers in electrical contact with each other, each layer comprising an electro-conductive substrate. These layers have a mesh or expanded metal structure and in a first embodiment the mesh is overlain by plastic insulating rails or spacers which prevent the strip being treated from contacting the electrode. The composite electrode was developed to replace particularly more customary lead electrodes which may dissolve into the solution placing lead ions in the solution and even small particles of lead metal as inclusions in the solution. While the composite electrode of Traini is somewhat similar in overall concept as a combination of an electrode with a surface shielding provided by a dielectric material on the surface of a composite electrode, its implementation is completely different in that a unitary open-web, plastic mesh mounted on a processing line as a separate shield between the workpiece and the electrodes is not disclosed.
U.S. Pat. No. 4,853,099 issued Aug. 1, 1989 to G. W. Smith discloses a so-called gap coating apparatus and process in which a relatively small elongated gap is established through which coating solution is passed at a high rate. It is said that the ultra high flow rate allows very high current densities. It is stated the process is not well suited for chromium plating, because high current densities do not increase the plating out of chromium.
U.S. Pat. No. 4,931,150 issued Jun. 5, 1990 to G. W. Smith, discloses a so-called gap-type electroplating operation in which a selected area of workpieces is coated by forming an electrode closely about such so-called gap and passing electrolytic solution through the gap at a high rate. It is stated that the ultra-high volume flow assures the removal of gas bubbles, the maintenance of low temperature and high solution pressure contact with the anode surface and a workpiece surface. It is stated that gaps approaching two and one half inches can employ the invention, but the gap would preferably be smaller, but at least 0.05 inches in width. It is stated that a fresh plating solution having a controlled temperature and no staleness is available at all times in the gap for uniform plating and while in high pressure contact with the surface of the gap. In practice, the plating solution is forced in a vertically upward direction so that any gas generated by the electrolysis in the gap migrates upwardly in the same flow direction as the plating solution is being driven and, therefore, can readily escape. It is also stated that chromium is difficult to use in the invention because chromium deposits slowly regardless of current density so that the deposition is slow and the advantages of gap plating are not fully attained.
While other processes and apparatus have, therefore, been available to remove hydrogen bubbles from cathodic coating surfaces, sever and remove dendritic material in coating processes such as the electrolytic coating of chromium and prevent depletion of the electrolytic solution and to some extent, establish a desirable coating gap between the coating electrode and the material being coated, all such prior processes have had drawbacks and none has been effective to accomplish all four or even two or three of the disclosed aims of the present invention by themselves. The same is true, generally, with respect to anodizing of workpieces including the anodizing of aluminum strip, aluminized steel, aluminum foil for capacitor production, aluminum for lithography, and other suitable metals such as magnesium and copper, various aluminum alloys and even stainless steel where a colored oxide on the surface is desired. Likewise, while electrolytic cleaning processes have been available, none have had the efficiency conferred by the use of resilient wiping blades and open web, plastic mesh separators during the electrolytic cleaning of strip and the like.